This invention generally relates to sootblower devices which are used to project a stream of a fluid cleaning medium against internal surfaces of large scale combustion devices for cleaning the surfaces. In particular, this invention concerns a sootblower lance tube which can be readily adapted for use with different types of fluid cleaning media.
Sootblowers are used to project a stream of a fluid cleaning medium such as water, air or steam against internal surfaces of a combustion device such as large scale boilers to cause a range of slag and/or ash deposits to be removed through a process of mechanical impact and thermal shock. Various types of sootblowers are used. One general category of sootblowers is known as the retracting type. These devices have a retractable lance tube which is periodically advanced into and withdrawn from the combustion device, and may be simultaneously rotated such that one or more nozzles on the lance tube project a jet of cleaning medium which traces an appropriate cleaning path. In typical retracting sootblowers, a feed tube is held stationary relative to the sootblower frame which sets outside the combustion device. One end of the feed tube is supplied with the cleaning medium through a poppet valve. The lance tube slidably over-fits the feed tube and its longitudinal sliding and rotational motion is controlled by a carriage which moves along tracks on the sootblower frame. The cleaning medium supplied to the feed tube in turn pressurizes the hollow interior of the lance tube. The cleaning medium escapes from the lance tube through one or more nozzles which direct the spray against the surfaces to be cleaned. At the conclusion of a cleaning cycle, the lance tube is retracted and withdrawn from the combustion device to avoid exposure to the intense heat and/or corrosive atmosphere which would degrade or destroy the lance tube.
Various fluid cleaning media are used in sootblowers as a function of the particular cleaning requirements. Gaseous or vaporous fluids such as steam and air are used in many applications. In other instances a liquid cleaning medium, typically water is used, depending upon the sootblowing requirements. For simplicity, throughout the remainder of this description, the two categories of cleaning media will be referenced to inclusively as "steam" or "water". Lance tubes are typically manufactured exclusively for a particular type of sootblowing medium. Blowing of steam requires a nozzle specially configured for efficiently discharging such compressible media. In the case of water used as a sootblowing medium, specially designed nozzles are used which typically have a much smaller cross-sectional flow area than those used for steam. Unfortunately, a single nozzle configuration is not well suited for use with both steam or water due to the significant difference in the fluid characteristics of those media.
In some sootblowing applications there is a need to periodically change the sootblowing medium being used in response to changing cleaning requirements within the combustion device. In the past, a change of the sootblowing medium would typically involved a complete change of the lance tube, with one having nozzles intended for steam and another especially designed for spraying water. Designs having interchangeable nozzles have been considered but are problematic since the lance tube operates in a hostile environment, and accordingly, threads or other precision mating surfaces tend to become degraded in service, making removal and replacement of special nozzles difficult. Examples of such convertible designs include lance tubes having threaded-in nozzle bushings, and a design in which the tip of the lance tube is threaded to the main lance tube section. These approaches are however, unsuitable for the reasons mentioned above.
In the absence of a means for changing the flow nozzle, switching the sootblowing medium suffers from the disadvantageous requirement that the entire lance tube be removed from the sootblower, and thus the task of replacing the lance tube is a significant and time consuming effort and further takes the cleaning equipment out of service for an extended period.
One approach toward providing a convertible sootblower lance tube is described by U.S. Pat. No. 4,209,028 assigned to the assignee of the present invention. That patent describes a sootblower lance tube adapted for discharging steam or water which has a pair of axial displaced nozzles, one designed specifically for each of the cleaning media. A thermostatically operable valve is inter-posed between the nozzles which closes off the distally located steam nozzle when liquid at a temperature lower than that of steam is in the lance tube. Although that design is believed operable, it is perceived to have several shortcomings. In particular, actuation could be hampered by internal fouling of the lance tube. In addition, the mechanism has a number of moving parts, giving rise to reliability concerns. That unit moreover, responds over time to a change in the fluid cleaning media being supplied. Accordingly, there is some actuation time lapse following a change in media. Due to its automatic operation, the system according to the previously mentioned patent would not provide a positive indication that a change in nozzle discharge has occurred, thus making affirmative verification of proper operation difficult. Fluid supply pressures may also have to be limited in utilizing a design according to the previously mentioned patent since the moveable valve described therein must close off high pressure water flow when switching from steam to water.
In view of the foregoing, there is a need to provide a sootblower lance tube which is readily adapted for discharging steam or water sootblowing media. Ideally, such a conversion could be made with a minimal down time and would be performed using mechanisms which would withstand the hot and corrosive environment in the interior of the combustion device.
In accordance with the present invention, a sootblower lance tube is provided with means to enable such rapid conversion between cleaning media. This is achieved by providing a pair of nozzle groups, with one or more steam nozzles being placed near the distal end of the lance tube, and one or more water nozzles being located longitudinally displaced from the steam nozzles toward the proximal end of the lance tube. Between the two groups of nozzles is placed a fluid flow control means, which in one embodiment incorporates a plug element which can be externally manually removed and replaced in a plug block mounted along the lance tube. At least two different plug element configurations are implemented, one of which is intended for steam discharge having a low restriction flow passage therethrough which allows steam supplied to the hollow interior of the lance tube to readily flow to the distal steam nozzles. Although a portion of the steam may also discharge from the water nozzles in some applications, this flow is a small proportion of the total output, given the relatively small diameter and consequently higher fluid flow restriction posed by the water nozzles. This flow is however useful in keeping the water nozzles cleared. Another plug element for water discharge provides a relatively high restriction flow path which causes water supplied to the lance tube to flow through the water nozzles. Preferably for most applications, a proportionately small flow of water is however, permitted to pass to the steam nozzles to provide a cooling effect for the distal end of the lance tube. In a preferred embodiment of a plug element for water cleaning, a spray nozzle is provided in the plug element which disperses water on the inside surfaces of the distal end of the lance tube to enhance the cooling effect provided.
In a second embodiment of this invention the fluid flow control means comprises a manually operable valve element in which a gate plate is rotatable within a plate block between two positions. In one position, the gate plate allows for a free flow of fluid through the valve assembly for steam cleaning. In a rotated second position, the flow of fluid is substantially restricted for use with water with the exception of a minute flow for cooling purposes as in the prior embodiment.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.